Apple released iOS 6 beta 3 for iPhone 4S, iPhone 4, iPhone 3GS, iPad 3, iPad 2 and iPod touch 4G, which is a developer release whereas the final iOS 6 will be available to general public in this fall.
The latest iOS 6 beta build number is 10A5338d which could grabbed through iOS Dev Center.
See also:
iOS 6 New Features